导入 ImageIO框架

 #import <ImageIO/ImageIO.h> 

自己写一个返回Size的方法

 - (CGSize)getImageSizeWithURL:(NSURL *)url
{
    CGImageSourceRef imageSource = CGImageSourceCreateWithURL((CFURLRef)url, NULL);
    CGFloat width = 0.0f, height = 0.0f;

    if (imageSource) 
    {
        CFDictionaryRef imageProperties = CGImageSourceCopyPropertiesAtIndex(imageSource, 0, NULL);
        if (imageProperties != NULL)
        {
            CFNumberRef widthNum  = CFDictionaryGetValue(imageProperties, kCGImagePropertyPixelWidth);
            if (widthNum != NULL) {
                CFNumberGetValue(widthNum, kCFNumberFloatType, &width);
            }

            CFNumberRef heightNum = CFDictionaryGetValue(imageProperties, kCGImagePropertyPixelHeight);
            if (heightNum != NULL) {
                CFNumberGetValue(heightNum, kCFNumberFloatType, &height);
            }

            CFRelease(imageProperties);
        }
        CFRelease(imageSource);
        NSLog(@"Image dimensions: %.0f x %.0f px", width, height);
    }
    return CGSizeMake(width, height);
}